1. Field of the Invention
This invention relates to a process for the manufacture of catalysts for the reduction of oxides of nitrogen from exhaust gases and in chemical air cleaning processes in which a catalytically active material containing iron ores, chromium ores and/or zeolite is placed in contact with a carrier means having a series of openings; e.g., wire mesh, expanded or perforated metal or any type of grid-like structure, to form a catalytic member. The carrier means is etched with an acid etchant before forming the catalytic member or, instead, the catalytic member is etched with an acid etchant. The catalytic member is bonded by a thermal treatment; e.g., drying, tempering and/or fixing. This invention also relates to catalytic members and products produced by the process.
2. Description of the Prior Art
U.S. Pat. No. 4,806,427, issued on Feb. 21, 1989, corresponding to German Patent No. DE 35 26 383 C1, discloses a process of the type described above, in which a so-called composite catalyst is obtained; i.e., a catalyst whose mechanical structure is improved by the inclusion of a perforated metal support, for example. In accordance with this method of the prior art, the metal support is etched with acid, either by bringing the metal support into contact with a mixture of catalytically active material and acid, or by previously etching the metal support by immersing it in acid. In this method of the prior art, sulfuric acid is used as the etching acid.
In the prior art process, the catalytically active material can comprise natural raw materials such as iron ore, chromium ore or zeolite and/or synthetic substances and/or industrial by-products such as slags, sludges or scale. It is also possible to add activators, e.g. elements or oxides of the 7th and 8th principal group of the periodic system, to these catalytically active materials.